High frequency tuning apparatus



Feb. 19, 1957 R. R. ENGLISH 2,782,315

1 HIGH FREQUENCY TUNING APPARATUS Filed oct. 1e, 1951 4 sheets-sheet 1Lv Feb. 19, 1957 R, R ENGLlsH 2,782,315

HIGH FREQUENCY TUNING PPARATUS Filed 000. 16, 1951 4 Sheets-Sheet 2 INI/EN?. fafa?? 627;@ ad

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HIGH FREQUENCY TUNING APPARATUS 4 Sheets-Sheet 5 .Filed Oct. 16, 19 51 :@7919 MMINVENTOR.

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y/Z/. 'Rm Jl mm I l l 1 l I l I l I I I l I I I United States Patent O 2,782,315 HIGH FREQUENCY TUNING APPARATUS Robert R. English, Itasca, ill., assignor to Oak Mfg. Co., Chicago, lll., a corporation of iilinois Application Getober 16, 1951, Serial No. 251,570

7 Claims. (Cl. Z50-40) This invention relates to an electrical apparatus and, more particularly, to a tuner for use at high frequencies. Tuners forming the subject matter of this application are adapted for use at frequencies ranging from about 2() megacycles up to as high as i000 megacycles and even higher.

Tuners for use at such high frequencies may take on a wide variety of forms and operate in a number of dilerent ways. The tuners forming the subject matter of the present invention are of the type where the circuit parameters, such as capacitance or inductance, are varied in a continuous manner to cover the entire operating range of the tuner.

Tuners, as a rule, are disposed in metal frames generally resembling the frames used in variable condensers. Such frames fulfill both mechanical and shieldingfunctions necessary for proper operation of tuners. As the frequency, at which the tuner operates, increases, it has been found that objectionable operating effects are present in tuners of the type available in the art. Thus for example, the tuners with which we are concerned generally have a metal shaft carrying rotor elements generally resembling the rotor blades of a variable condenser.

Customarily, such rotor blades are secured to a metal shaft and the rotor blades themselves cooperate with.

stator elements of suitable design and shape. The stator elements, from an electrical angle, are not symmetrical with respect to ground. Thus if the instantaneous radio frequency potential of the stator as a whole is considered,`

have relied upon the metal frame to form a part of the tank or tuning circuit. This results from using the frame as a ground for two or more different points of the tuning circuit between which points there exists R. F. potential differences. The tuner frame, therefore, forming part of thevcircuit would itself require shielding and when y,the frame was mounted upon a metal chassis, the entire tuner behaved differently than when the tuner .was by itself.

As a result, ground currents in the frame and metal shaft exist and alter, in an undesirable fashion, the characteristics.L Such eifects are noticeable at frequencies as low as around 20 megacycles.

At frequencies of several hundred megacycles, it has been found that ythe physical dimensions of the frame are substantial in terms of operating wave length..`

The result has been that the combination `of nonsymmetrical stator arrangement to ground together with a metal shaft in a metal frame has given rise to undesirable resonance phenomena. In such case, it frequently occurs that the tuner will have yno outputat certain frequencies within the operating range thereof and upon examination and investigation it will be found that such certain frequencies appear to be absorbed within the frarne-workof the system` and thus result in atotal dissipation of energy.

The invention, vto be described in detail later, makes it rice possible to have a tuner operating in a conventional metal frame. The new tuner is provided with rotor elements insulated from the frame together withfa split-stator construction. As a result, the stator elements of the tuner are, electrically speaking, symmetrical with respect to the rotor and with respect to ground. Hence, the effects of such capacitance to ground and capacitance to the rotor elements will be more nearly balanced and uniform in the new tuner than in prior art tuners of the same general type.

For the iirst time,l a continuously variable type of tuner construction is provided wherein each tuning circuit is electrically complete in itself apart from theframe. Any desired point on the tuning circuit may be metallically connected to the frame. No part of the frame, however, is connected as an integral part of the tuning circuit and hence the frame is never connected to any two points of one tuning circuit between which an R. F. difference of potential exists. It is understood that infunctioning as anelectrostatic shield, the frame will have slight currents (as compared to the circuit currents) and thus will have some potential differences therein. This, however, is inherent in shield action and is different from the integration of the frame into the tuning circuit by metallic connection thereto at different points.

in addition to improving the operating characteristics of the tuner, the invention frees the new tuner from many limitations arising out of the necessity, in prior tuners, of locating the ground at a certain part of the tuning circuit. In tuners embodying the present invention, ground may be established at any part thereof.

While the invention may be applied'to various kinds of tuners, it may be applied with particular advantage to two forms of tuners.- Thus, one form of tuner to which the invention is applied is of the so-called mixed capacitance and inductance variation type where both capacitance and inductance are simultaneously varied. The other form of tuner to which the invention may advantageously be applied is of the kind having fixed inductance but variable capacitance. Both forms of tuners, however, are of the kind that are free of any wiping contacts.

In both-forms, the tuner includes a metal frame having an insulating shaft, or a shaft insulatingly supporting rotor elements, secured from rotation therein. A metal frame ,is made to support any desired number of tuning sections, each section being shielded from other sections, this being similar to a gang variable condenser. Each tuning section comprises at least one blade rotor of metal having the same general shape as the rotor blades in a variable condenser. The stator for a tuning section consists of metallic elements joined together metallically to form separate lumped capacitor and lumped inductor portions. The stator elements forming part of the capacitors are split electrically so that the lumped capacitor portions are divided into two equal parts, these two capacitor portions having an electrically common rotor. The inductor part of a tuning section is metallically continuous and is connected between the two stator capacitor plates. Means for coupling to the tuner sections are provided.

In one form, the inductor part of a tuning section is variable simultaneously with the capacitor part.` In the other form of the invention, the inductor part of .a tuning section is iixed and does not cooperate with the rotor elements as is true in the variable inductor type.

In order that the invention may be understood, it will now be explained in connection with the drawings, wherein:

Figure l isa diagrammatic showing of a circuit illustrating the principle of the present invention;

Figure 2 is a top plan view of a tuner having one tuning section embodying the present invention;

Figure 3 is a side view of the tuner of Figure 2;

Figure 4 is a section on line 4-4 of Figure 2;

Figure 5 is a sectional detail on line S5 of Figure 2,

Figure 6 is a top plan view of the tuner similar to Figure 2 but showing the rio-tor in a different position;

Figure 7 is a sectional view on line 7--7 of Figure 6;

Figure 8 is an exploded View showing certain of the elements of the tuner of Figures 2 to 7 inclusive;

Figure 9 is a top plan view of a modified form of tuner embodying the present invention;

Figure 10 is a sectional view on line 10-10 of Figure 11;

Figure 11 is a sectional view on line 11-11 of Figure 9- Fighre 12 is a sectional view on line 12-12 of Figure 9;

Figure 13 is a sectional view on Aline 13-13 of Figure 9;

Figure 14 is a sectional view on lline 14--14 of Figure 9;

Figure 15 is a perspective ydetail of the stator part of the tuning section for an oscillator circuit;

Figure 16 is a perspective exploded view of the tuning elements of a tuning section;

Figure 17 is a diagrammatic showing of a circuit em bodying the modified form of tuner shown in Figures 9 to 16.

Figure 1 is a diagrammatic representation of a tuner embodying one form of the invention where both capacitance and inductance are simultaneously varied. Such a tuner has some desirable characteristics, the variation of the -two parameters rendering tuning faster and providing a substantial tuning range.

Referring now to Figure 1, there is shown an inductor generally indicated by numeral 10. Inductor 10 may consist of a number of separate loops having the required physical dimensions. Inductor 10 is preferably of the type where the inductance is varied by controlling the coupling between the turns of the inductor and movable rotor plate or plates.

As is clear in Figure 1, the various turns of inductor` 10 are connected in series to provide terminals 11 and 12 for the inductor as a whole. Connected to terminal 11 by a suitably short connector 13 is stator plate 15 -of variable condenser 16. Similarly, terminal 12 lof inductor 10 is connected by connector 18 to stator 19 of variable condenser 20. Condensers 16 and 20 respectively have rotor elements 22 and 23 connected electrically and mechanically together. Rotor elements 22 and 23 may actually be one common plate or blade. As will be apparent later, in connection with the description of Figures 2 to 8 inclusive, rotor plates 22 and 23 also function to vary the inductance of 10 by linking the turns of the inductor.

Although Condensers 16 and 20 are symbolically shown as having each one stator and one rotor plate, in practice, each of these Condensers may yconsist of a number of stator and rotor elements, forming a number of condensers whose stators are connected together, respectively.

Similarly, condenser 2i) is constructed in like fashion. Condenser 16 and 20 are preferably similar mechanically and electrically to provide symmetrical arrangement of capacitor elements, although this is not essential.

It is clear therefore, that there arc provided two separate capacitors having a common rotor. The capacitors are varied together in the same sense; i, e., they both increase or decrease simultaneously.

As will be apparent later, in connection with the detailed description of the construction as shown in Figures 2 1to 8 inclusive, each tuning section has stator elements forming a lumped inductance and stator elements also forming part of two lumped capacitances. Because of the arrangement of rotor plates with respect to capacitor plates in this particular form, it is necessary that all rotor plates in a tuning section be metallically connected together so as to be at substantially the same potential with respect to ground. Each tuning section could reduce to a. minimum of one rotor blade, two stator capacitor plates and one inductor element.

Referring now specifically to Figures 2 to 8 inclusive, there is shown metal frame generally indicated by numeral 30 and having bottom 31, ends 32 and 33 and sides as desired. The amount of frame metal at the sides and the necessi-ty for a metal cover at the top will be dictated by the ultimate mounting of the tuner with respect to other circuit components, and the amount of shielding necessary. It is understood, that the frame is of heavy metal, such as steel, rigid enough to provide adequate support. In general, this frame may resemble the frame used in gang condensers. Between adjacent tuning sections there Will be shield plates grounded to the frame.

Rotatively supported in sides 32 and 33 of the frame is insulating shaft 35. This shaft is rotatively supported in any suitable manner, the insulating shaft itself being preferably provided at the ends thereof with metal portions for cooperating with bearings carried by the frame. In general, the mounting of the shaft is similar to a variable condenser mounting and presents no problems. Shaft 35 itself is of solid insulating material, such as Bakelite or any other material having desirable properties in a high frequency circuit.

Suitably secured in shaft 35 are a number of rotor blades generally indicated 'by numeral 37 and differentiated from each other by letters a, b, and the like.

The frame itself is preferably long enough to accommodate 'a number of tuning sections. These tuning sections may be similar except for one tuning section which may control an oscillator or mixer circuit and which, in practice, will cover a somewhat `different frequency range than other tuning sections. inasmuch as the mechanical construction of the various tuning sections will generally be similar, the description herein given is limited to one tuning section.

Rotor blade 37 is of suitable material and is provided with a surface coating having low ohmic resistance. Thus, if the Iblades are of steel or any other metal `except copper or silver, it is preferred to have the surface of the rotor lblades of silver or copper. The blades have a generally semi-circular configuration, although this may be varied -to 4change tuning characteristics.

Each blade is secured to the insulating shaft in any dcsired manner, the usual arrangement being to have annular slots in the shaft into which the blades are forced. In case there is more than one blade, connecting member 39 is provided along the surface of the insulating shaft to provide good electrical `contact between the various rotor blades of one `tuning section.

In general, it is preferred to insulate one rotor group in one tuning section from the other rotor group in another tuning section. However, in some cases it may bc desirable to maintain the rotor blades in all tuning sections at the same potential. In all cases, however, the rotor blades are insulated from the frame and no wiping or other contact providing any metallic connection is provided between the rotor blades and any stationary portion of the entire tuner.

As shown here, a tuning section is provided with eleven rotor blades numbered 37a to 37k, these blades being rotatively aligned and disposed generally in a manner resembling the rotor blades of `one section of a variable condenser.

Carried by the frame, at one side thereof, is insulating strip 42 extending lengthwise of the fratrie. A similar insulating strip 43 is carried by the frame on the other side thereof, these two insulating strips being disposed opposite each other and supporting all the stator elements. In general, insulating members 42 and 43 carry the stator elements in a similar manner, although the stator ele ments secured to these two strips are of different character.

Thus for example, insulating strip 43 has two series of apertures generally indicated by numerals 44 and 45 and each one in this series being specifically identified by letters a to j inclusive. The apertures in one series are disposed vertically above the corresponding lettered apertures in the other series in the position of the tuner as shown in Figure 3. Thus vaperture 44a is above 45a and so on. Apertures e and f are not used so require no reference thereto.

Each corresponding pair of apertures, that is two apertures in vertical alignment and identified by the same small letter, support the same capacitor plate for cooperation with the stator blades. The capacitor plates in the stator are all generally indicated by numeral d'7, the separate plates themselves being identified by letters n to i inclusive.

The main body of each capacitor stator plate d'2 is generally similar to the rotor blade, although variations in shape are possible to endow the tuner with different tuning characteristics. Thus each -stator plate generally consists of a semi-circular body having semi-circular cut-out portion 48 to clear the shaft and rotor connectors carried by the shaft.

Each capacitor stator plate is provided with a pair of tongues or fingers 49 and 50, these being vertically aligned when the plate is vertically disposed. Fingers 49 and 50 are adapted to regi-ster with and enter a pair of vertically `aligned apertures in insulating-support member 42. These lingers are then soldered or otherwise permanently `attached so that each plate is rigidly positioned.

Stator plates 47a to 47d and 47g to 47k are connected to for .i two groups of plates. Thus copper or silver lug 52a is connected between aperture 44a and aperture 4519. It is understood that these lugs are also soldered so that a good electrical connection between stator plates 47a and 47h is provided.

The two groups of capacitor plates are formed by omitting certain lugs. Thus lugs 52a, 5212 and 52e are provided. Then lugs 52g and 52h and 521' are also provided to connect the appropriate stator plates. It will thus be seen that there is a gap in the metallic connection between stator plates 47d and i7g. The stator plates in a group are all connected in parallel. Other means for connecting the plates of one group together may be provided.

To provide a metallic connection between the capacitor stator elements and the inductor stator elements to be described now, end capacitor stator plates 47a and 471 are shaped to provide connecting arcuate straps 57a and 57j. For convenience, strap 57a comes around the bottom of the shaft while strap 57j cornes over the top of the shaft. This, however, is not essential and the arrangement may be reversed or both straps may come over lthe shaft or under the shaft.

Connecting straps 57a and 57j each have fingers 66 `entering apertures in insulating strip 43.

insulating strip gi3 generally resembles insulating strip 42 and has two series of Superposed apertures generally indicated by numerals 60 and 61 and ranging individually from a to k inclusive. interconnecting lugs 62 are provided, these ranging from a to j inclusive to connect the ,successive inductance elements in series.

Referring now to Figures 2 and 8 specically, each individual inductor stator element consists of loop 65, the individual loops being separately identilied by letters .si to h inclusive. These loops are similar and consist of a strip having surfaces of good conductivity such as copper or silver. The loop consists of the outline of a semicircular plate such as used for the stator capacitor elements, the interior portion of the plate being punched out.

.it is understood that other shapes of loops are possible and the shape of the loop may be varied to suit require ments, corresponding to the shape of the stator plates or rotor blades or desired inductance variation characteristics. it is understood that each loop is so shaped as 4to clear the shaft., Each loop has its endsshaped to provide -fingers 66 an'd 67 engaging respectively the vertically 6 v aligned pair of apertures in the insulating plate 43. These loops are soldered in position and, by virtue of the lugs, are all connected in series to form a continuous lumped inductance.

Itis clear that straps 57a and 57j provide direct metallic connections from the free ends of the two capacitor stators to the terminals of the inductor sections. Ends 57a and 57j forming the junctions between the capacitor and inductor terminals, may constitute terminals for the tuning section of a tuner.

The tuning range `of the rotor is substantially degrees. Thus one end position of the tuner is shown in Figure 4 and another end position is shown in Figure 7. ln all other positions, the rotor symmetrically engages both the inductor and capacitor elements. Thus as capacitance is decreased, inductance is decreased with the rotor blades engaging both types of stator elements.

By having the capacitor stator plates electrically split to form two groups, substantial flexibility for connection to outside circuits is obtained. Thus, the entire rotor for a tuning section is electrically symmetrical to ground. The stator elements are also electrically symmetrical with respect to the rotor and with respect to ground. Hence, disturbances due to improper shielding or various capacitances to ground or any tendency to form resonant pockets or ground currents in the fra-me will be entirely eliminated or balanced out.

Furthermore, the tuning circuit for a section, including inductance and capacitance, is complete in itself, apart from the frame. The frame merely provides mechanical support and is a substantially pure electrostatic shield.

It is possible to connect either terminal of the inductance to ground or, in fact, to connect ground to the center of the inductance `and then have high potential connections tc the two ends of the inductor. lt is, of course, true that as soon as one end terminal of the inductor is grounded, then the electrical symmetry to ground is destroyed. However, the inherent symmetry of the entire tuner and the balanced distributed capacitances `make it possible to ground any part of the tuner with the assurance that proper' operation thereof will result.

It is also possible to ground the two ends of the inductor and use the center of the inductor as a high potential terminal.

lt is understood, of course, that the various circuit constants and parameters will have to be adjusted for the type of ground connection or connections to be established. It is also understood, that small trimmer condensers may be secured at appropriate places adjacent the capacitor elements to provide proper tracking, this, of course, being well-known in the art.

lt is also possible to connect the inductor loops in parallel. This will raise the tunable frequency and an equivalent construction using only one inductor loop may be substituted.

Referring now to Figures 9 to 16, an embodiment of the invention is shown wherein a iixed inductor and variable capacitors for each tuning section is provided. In general, the 'fixed inductor consists of a small loop of metal strip, the ends of which are shaped to form stator capacitor elements, Thus, one inductor loop terminates in a pair of separate stator condenser plates. Cooperating with both condenser' plates are one or more rotor blades. These rotor blades are preferably shaped to provide substantially symmetrical capacitor action simultaneously with both stator plates.

A metal frame for supporting the tuner comprises base 89 carrying front and rear walls 81 and 82, side walls 83 and 84 and top 85. Base 80 is simply a plate to cover the bottom of the box-shaped frame and, as is readily apparent from Figure ll, this is applied last.

Front and rear walls 81 and 82 are shaped to provide suitable journals for rotatively supporting shaft 87. Shaft 87 is of Ainsulating material. The interior of the frame is divided by plates 88 and 89 into thi'ee'cornpartyments, these plates being suitably Islotted at 90 (see Fig.

14) to accommodate shaft 87. Plates 88 and 89 are of metal and function as shield plates to divide one compare ment from the other, each compartment accommodating a tuning section. The shield plates may be bolted at 91 to top 85 of the frame. Other means of attaching the shield plates to the frame may be used.

Shaft 87 carries a pair of rotor plates for each tuning section. As shown in the drawing, the tuner has three tuning sections 93, 94 and 95. Tuning section 93 is an oscillator tuning section and diiers somewhat from the remaining sections 94 and 95, these last two being identical. For convenience, tuning sections 93 and 94 only will be described in detail and it will be understood that additional section 95 is substantially the same as section 94.

Referring to shaft 87, this carries a pair of rotor blades 98 and 99 for tuning section 93. The rotor blades carried by the shaft are the same for all tuning sections so that only one pair will be described in detail. Thus blades 98 and 99 are flat and are provided with slotted parts 100 adapted to be pressed into annular slots of shaft 87 to maintain the blades tightly in position. Blades 98 and 99 have the shape shown in Figures l2 and 16. As shown, these blades have a generally semi-circular main body portion 100 and an additional portion 101, the two portions having the general shape shown. The rotor shape should preferably be so designed that equal rotor areas cooperate with the two parts of the stators making up the split condenser plates. It is clear therefore, that the shape of the rotor blades may vary depending upon the particular shapes of the stator plates. The design of such plates is well within the skill of those versed in this art.

Cooperating with rotor blades 98 and 88 are stator condenser plates 103 and 104 (see Fig. l5), these two condenser plates forming part of an inductor loop generally indicated by numeral 105. Inductor loop 105, unlike the inductor loops for the remaining tuning sections, is divided into two parts, this being used in an oscillator circuit. Thus inductor loop 105 has sides 106 and 107 and rear portions 108 and 109, these rear portions being iiat and spaced from each other to provide a tixed condenser having the rear portions as plates there of. vln order to maintain rear portions 108 and 109 rigidly in position, insulating block 110 is disposed therebetween and the assembly is maintained by insulated rivets 111. Plates 108 and 109 are connected to the grid and anode electrodes of a suitable vacuum tube functioning as an oscillator. length at which the tuner operates, it is desirable to reduce the length of leads to the vacuum-tube electrodes to a minimum. Accordingly, plates 108 and 109 are each supplied with clips 113 and 114 of copper or other suitable metal. operate with the opposed metal sides of plates 1055 and 109 to accommodate the pins of vacuum tube 116. Tube 116 may be of any suitable type of vacuum tube which may function as an oscillator and the formation of clips 113 and 114 will depend upon the disposition of the electrode pins in the base of the tube. The remaining tube electrodes consisting of cathode and heater leads will be accommodated by a conventional but mutilated vacuum tube socket 117, this mutilated socket together with clips 113 and 114 accommodating as many of the tube pins as are required to establish tube connections.

The inductor loop 'and plates forming the condenser-s are of sufficiently heavy gauge metal so that the device is mechanically stable. The surface of the material has low electrical resistance and this may generally be obtained by having a silver surface. The inductor material itself may be formed of copper, or brass, or bronze. In order to support the inductor structure mechanically in position, there are provided ears 119 and 120, these ears being suitably apertured and extending outwardly away Because of the short wave Such clips are shaped so that they co- '8 from the interior region of the inductor loop. Bolts 121 and 122 extend upwardly from ears 119 and 120 and are maintained in position in stand-oli insulators 123 and 124 secured in metal top 85 of the housing. Other means for insulatingly mounting the inductor loop portions within the frame may be provided.

It is desirable to provide trimmer condensers for adjusting the minimum or maximum capacitances at the variable condensers. Accordingly, condenser plate portions 103 and 104 have condenser plate ears 126 and 127, these being bent inwardly over the region enclosed by the loop. It is understood, however, that both the mounting ears and the condenser ears may be bent in reverse manner if desired. Cooperating with two ears 126 and 12'7 is variable grounded trimmer plate 128 carried by bolt 129 supported in top 85 of the housing. Variable plate cooperates with both ears 126 and 127. lf desired, each ear 126 and 127 may have its own individual variable capacitor plate.

Referring now to tuner section 94, the rotor blades carried by the shaft are generally similar to the rotor blades in the oscillator tuning section except for the fact that the blades may have different areas or the shape may be somewhat different. However, the general construction is similar in that two rotor blades are preferably provided on opposite sides of the condenser plates forming the ends of the tixed inductor. It may be observed that the two rotor blades may be replaced by one rotor blade having the desired area. However, it is preferred to have a pair of blades on opposite sides of the fixed capacitor plates. Thus rotor blades 98a and 98b for tuning section 94 cooperate with condenser plate portions 10311 and 1031) of inductor 105:1. Inductor 105a differs from inductor 105 in that rear portion 108e is complete and extends across between sides `106a and 107e.

Mounting ears 119a and 120:1 are provided, these ears being apertured but extending inwardly over the region enclosed by the inductor loop. The ears are engaged by bolts and insulator in substantially the same manner, the inductor being rigidly supported by cover portion 85 of the housing. It will be observed that trimmer condenser ears 12651 and 127e cooperate with a variable trimmer plate 128e in a manner similar to the tuning d section previously described.

=There are also provided some additional trimmers to cooperate with the inductor portion of the stationary element to vary the inductance. Such trimmers vary the losses of the inductors and thus control the inductance of each loop. Thus each tuning section has bolt 130 of insulating material insulatingly threaded into a suitable part of the frame so that the bolt may be adjusted to move inwardly or outwardly from the inductor loop. Nut 132 cooperates with bolt 130 for locking the bolt in desired position. The top end of the bolt may be slotted so that the bolt may be adjusted from outside of the tuner frame. Each trimmer bolt carries metal trimmer ring 134 attached to the head, such rings being cut to desired size and then to desired shape.

yIt will be evident that in the form of the invention shown in Figures 9 to 16 inclusive, that the single loop formed by the inductor has a voltage or potential node existing at a spot approximately midway between the ends of the metal strip forming the condenser stator plates. At this voltage node, current is a maximum and voltage or potential is a minimum, the two being out of phase. As the end of the metal strip is approached, the phase angle between potential and current decreases so that at the very ends of the loop, both potential and current are normally in phase, the potential being at a maximum while the current is at a minimum. It will thus be evident that the location of the ears for supporting the inductor strip is such that a minimum of radio frequency losses will occur. Instead of two ears, only one ear 'for mounting the inductor ele- 9T ments may be provided.V However, it-isfpreferred to have the two ears and these ears being `close to the potential node will provide a balanced low loss support for the structure.

Itis understood that in connection with the vacuum tube pin clips used on the oscillator section 4of the tuner and illustrated in Figure 8, the location of the pins` will be such as to dispose the control vgrid and anode connections on opposite sides of the voltagenode. In this form of inductor loop, the overlying ends form a coupling capacitor, the voltage node being located in space between theoverlying ends. Because of the close proximity to the voltage node, there will be suiicient leeway in locating these connections on the inductor so that these clips and inductor may be prefabricated as a unit. Theoretically, of course, thepotential-on the control grid is usually lower than on the anode of the vacuum tube oscillator so that the control grid connection should be closer to the potential node than the anode connection. However, the actual length of leads from the inductor to the actual electrode within the tube envelope will be important and, in practice, the differences between the grid and anode points of connection are negligible. Furthermore, the rate of change of peak potential from the minimum value at the node and increasing towards the ends of the inductor is rather slow in the vicinity of the nodes so that the region near the node is not critical.

Means are provided for connecting the tuner to a high frequency circuit and also for interconnecting the various tuning sections among each other. These means are conventional and generally take the form of so-called printed circuits. As is well known, the term printed circuits covers a variety of circuit layouts in the form oi a thin vtilrn or sheet of metal upon an insulating base. Thus such circuits may consist of copper stampings suitably cemented or attached to a strip of insulation or may consist of printing or etching metal films upon solid insulating material.

Thus referring to Figures l() and l1, lead-in wires 140 and 141 forming part of a conventional open wire line may enter into the interior of housing 84 through any suitable aperture or in any desired manner. Such a line terminates at insulating strip 143 disposed in tuning section 95 and attached to the housing in any suitable manner. insulating strip 143 contains a circuit element such as inductance 144 disposed thereon and suitably designed to couple to the inductance loop for that particular tuning section. insulating strip 146 extends between tuning sections 94 `and 95 `and has imprinted or otherwise attached thereto a suitable coupling element for connecting the inductance elements of the two tuning sections.

Tuning section 94 also has insulating strip 148 upon which there is disposed a suitable coupling circuit 149. Coupling circuit 149 is connected by wires 150 to pick-up unit 151 in oscillator tuning section 93. Two wires as shown are provided for connecting tuning section 94 to a television receiver or other device to be tuned. One of these wires is shown as grounded to the frame. However, an open or other line may be used and the frame may be symmetrical to both such wires, with the ground as neutral. it is understood that the various wires and insulating strips, carrying the coupling circuits between tuning sections pass through suitable clearances in the housing and partition and are suitably attached to the housing so that these elements are disposed in xed predetermined position with respect to the various inductance elements. Thus, in the case of 4oscillator tuning section 93, the energy from the oscillator is picked up in the circuit upon insulating strip 151 and transmitted to circuit 149 in tuning section 94. The coupling between tuning sections is similar to other tuners.

ln connection with Figures 9 to 16 inclusive, it is possible to increase the number of plates forming the tuning .condenser part of atuning section. Thus Aadditional platesgto'103 and. N14-may be provided, these plates being soldered to the inductor loop so that a number of spaced parallel plates extend inwardly toward each other. It is understood that the number of plates will be equal for 103 and 164. The additional plates will require additional rotor plates, one rotor plate operating between two adjacent stator plates for the 193 group and also for the 101i group. The end rotor plates may be on the outside of the stator plates in which case a rotor plate will cooperate with only one stator plate for each group. ln all cases, the capacitance for both Sections 103 and 104 simultaneously increase or decrease. Also the additional rotor plates are all insulated from each other.

Thus referring to Figure 17, inductor 205 has capacitor plates 203, 203er at one terminal thereof and plates 2M and 26Min at the other. Cooperating with these stator plates are rotor plates 201e, 20117 and 201C. These rotor plates are insulated from the frame and are preferably insulated from each other. it is understood that rotor plates for one tuning section are insulated from rotor plates of other tuning sections.

Best results in all cases are obtained by using an insulated shaft. However, it is possible to use a metal shaft with the rotor plates mounted so as to be insulated therefrom as by using insulating sleeves over the shaft. In the latter case, it may be advantageous to insulate the shaft from the frame proper as by mounting the shaft journals on insulating blocks.

In the structures described, the tuning circuits are individually complete without recourse to the frame. This is true even though the trimmer condensers may have one plate grounded. Thus the trimmer plate may be grounded or may be insulated from ground. If grounded, the trimmer plate wili always be at true R. F. ground potential. in other words, there will never be any tank R. F. potential difference between a grounded trimmer plate and any other part of the frame.

Other uses for the tuner than in receivers are possible. Thus the new tuners may be used in testing systems, transmitters, or the like.

What is claimed is:

l. A high frequency tuner including a tuner section comprising sheet metal shaped to form a one-turn inductance loop having the general shape of an incomplete thin walled and rectangular pipe length, the rectangular section having opposed short and long sides, one long side being broken at the center to form a pair of stator plates, a shaft perpendicular to the planes containing the opposed long sides, said shaft lying outside of the region within the loop, at least one metallic rotor plate insulatingly carried by said shaft for rotation in a plane lying between the opposed long sides and parallel thereto, Said rotor plate having one electrically unitary plate portion intermeshing the two parts of the stator plates simultaneously and symmetrically for capacitance variation, said rotor plate having the part adjacent the shaft at all times outside of the loop and substantially ineffective for tuning.

2. The construction according to claim l wherein means are provided for mounting said inductance loop at portions near the voltage node.

3. The construction according to claim l wherein two similar parallel rotor plates are provided on opposite sides of the stator plates, said rotor plates being elec-- trically insulated from each other.

4. The construction according to claim l wherein small ears are formed from the inductance loop metal at regions Where the stator plates are provided and wherein a frame for housing said tuner is provided and wherein at least one trimmer plate is carried by said frame for simultaneous cooperation with said ears for adjusting the minimum capacitance of the unit.

5. The construction according to claim 1 wherein ears` are formed from the inductance loop metal at the ends` l 1 where the stator plates are provided, said ears being bent to lie in one plane normal to the plane of the stator plates and wherein a frame for housing said tuner is provided and wherein at least one trimmer plate is carried by said frame for cooperation with said ears for adjusting the minimum capacitance of the unit.

6. The construction according to claim 1 wherein a metal slug is provided and means for mounting said slug for adjustable insertion into the region within the loop and clear of the rotor plate, said slug being adapted to trim the inductance value of the loop.

7. The construction according to claim l wherein the rotor part adjacent the shaft is slotted so that the rotor plate may be slipped into position on the shaft by moving the plate in its own plane.

References Cited in the tile of this patent UNITED STATES PATENTS Scofield Feb. 14, 1933 Harvey Feb. 1, 1944 Billiard Feb. 8, 1944 Toth Feb. 26, 1946 Weiss June 17, 1947 Landmann Mar. 30, 1948 Davis et al Dec. 20, 1949 Hibbard Dec. 27, 1949 Page Feb. 6, 1951 Kach et al Feb. 20, 1951 Schreiner May 12, 1953 FOREIGN PATENTS Great Britain Aug. 12, 1947 

